Storm Worm of a thousand faces

Authors of a particularly nasty piece of malware known as Storm Worm have yet again shifted their tactics. They are creating a flood of email hoaxes that try to install a bogus "applet" so victims can redeem membership benefits to clubs related to music, online dating and other interests.

The new emails bear subject headings such as "User info," "Membership support" and "Login information," and contain purported login credentials for sites that offer the gamut of services tailored to online music aficionados, cat lovers and poker players, according to this post by F-Secure.

Just as genetic mutations allow a particular type of caterpillar or breed of dog to better withstand virulent disease, the frequent changes in Storm improve its resiliency against attacks from rival criminal gangs and security providers. The tactical shifts are crucial since the success of Storm relies on the ability to dupe recipients into clicking on links and installing programs.

The most recent strain of Storm lures victims to sites that claim an "applet" needs to be installed so the user can login securely, according to this post by Johannes Ullrich, CTO for SANS Internet Storm Center.

The resulting applet.exe - which installs a backdoor on the user's machine - represents a case study in the benefits of adaptation. The binary morphs about every 30 minutes, making it particularly hard for antivirus programs to identify it as malware. Indeed, earlier on Tuesday, only 14 of 32 anti-virus programs detected a version of the applet Ullrich had downloaded. Later in the day, many of those laggards added definitions to flag the applet, but its ability to change so frequently means it may still be hard to detect.

"A lot of commonly used antivirus tools don't detect" Storm, Ulrich told The Reg. "The traditional signature approach that some of the antivirus vendors use really isn't all that useful anymore."

Programs that have the best chance of identifying the malware are those that use heuristics, or algorithmic rules of thumb, for identifying software that has a high likelihood of containing malware.

Like other Storm-related malware, applet.exe excels at cloaking itself from security researchers. The program actively monitors its host machine for VMware and will refuse to execute correctly if the virtualization software is detected. It also wraps itself in a packing container that makes it difficult to prevent outsiders from peering into the inner workings of the binary.

"You have to run it on a full physical system and that, of course, isn't as easy as running it in VMware," Ullrich said.

Those who scan the ports of machines infected by Storm, or who repeatedly download the Trojan have been subjected to DDoS attacks that have lasted for days.

The malware got its moniker after early versions lured victims to sites promising information about winter storms that were sacking Northern Europe. More recently, it started belching out toxic ecard scams.

Infections have shown a massive increase in recent weeks, being detected in 1.7 million unique hosts, according to internet security provider SecureWorks. That compared with just 2,817 hosts from January to May. The number of attacks blocked by SecureWorks has similarly skyrocketed, from 71,342 for the first five months of the year to 20.2 million since June.

Technically Storm isn't a worm because it doesn't spread automatically.

For all its sophistication, the malware relies on the oldest trick in the book, which is to socially engineer its victims. Let's be careful out there. ®